How do I make a door that is opened when 5 lights are activated?

You can do this

light1On = false
light2On = false
light3On = false
light4On = false
light5On = false


--However you are going to make them to turn on, goes here

if light1On == true and light2On == true and light3On == true and light4On == true and light5On == true then
-- Code goes here to open the door
end)

It's not working because you only check if the door is open once, at the very beginning of the game. What you need to do is send a check whenever a light changes, so the door can react accordingly.

The most efficient way to do this is to send the check whenever your other scripts activate the light (ex. if your script turns the light on when clicked, send the check through the same function). But since you didn't clarify how these lights were activated, we can just check the material itself with GetPropertyChangedSignal("Material").

--set up variables for the objects
local ActivationLights = game.Workspace.ActivationLights
local DarklightDoor = script.Parent

--handles updating the door to open/closed depending on the lights' material
local function updateDoor()
    if ActivationLights.Material == Enum.Material.Neon then
        DarklightDoor.Transparency = 1
    end
end

--connects the lights' material changing to the door's update
ActivationLights:GetPropertyChangedSignal("Material"):Connect(updateDoor)

I'm worried that ActivationLights isn't what you think it is since there should be 5 different lights you're checking. If ActivationLights is a Group/Model with the 5 lights inside it, you must use this code instead:

--set up variables for the objects
local ActivationLights = game.Workspace.ActivationLights
local DarklightDoor = script.Parent

--handles updating the door to open/closed depending on the lights' material
local function updateDoor()

    --loops through all the lights and checks their materials
    --isAllNeon is default to true, but turns false after seeing one light if it sees a light that's not neon
    local isAllNeon = true
    for _,light in pairs(ActivationLights:GetChildren()) do
        if light.Material ~= Enum.Material.Neon then
            isAllNeon = false
            break
        end
    end

    --checks if all the lights were neon
    if isAllNeon then
        --change the door to OPEN
        DarklightDoor.Transparency = 1
    else
        --change the door to CLOSED
        DarklightDoor.Transparency = 0
    end

end

--connects every lights' material changing to the door's update
for _,light in pairs(ActivationLights:GetChildren()) do
    light:GetPropertyChangedSignal("Material"):Connect(updateDoor)
end